. There is increasing evidence that there are human health benefits from the consumption of omega-3 (n-3) fatty acids. These benefits include amelioration of some pathological states (cardiovascular disease and neoplastic growth) and provide an essential dietary compound required for normal growth and development in humans. While the mechanisms of these benefits are unknown it is possible that they arise from an impact of these fatty acids on intercellular signalling mechanisms that utilize lipid mediators derived from membrane phospholipids. The primary objective of this proposal is to determine the nature of the impact of n-3 fatty acids on signal transduction pathways in HL-60 cells. Undifferentiated HL-60 cells, and HL-60 cells differentiated with dimethylsulfoxide (neutrophil-like cells) and phorbol esters (macrophage-like cells) will be used.These cell models will be supplemented with oleic (n-9), arachidonic (n-6), eicosapentaenoic (n-3) and docosahexaenoic (n-3) acids. Supplemented and unsupplemented cells will be stimulated with three physiologically relevant stimuli (formylmethionylleucylphenylalanine, C5a and platelet activating factor, PAF) and three inflammatory responses examined (respiratory burst degranulation and PAF biosynthesis). In those instances where n-3 fatty acid supplementation causes changes in the response, cellular lipids will be extracted and analyzed to determine the molecular species of phospholipids present. Cells will be extracted at intervals following stimulation and the lipid mediators generated will be analyzed. By comparing alterations in the responses with alterations in the mediators generated it will be possible to determine how n-3 fatty acids affect signal transduction systems in HL-60 cells.